The present invention relates generally to defoamer compositions, and more particularly to water-based compositions for controlling foam in pulp and paper mill operations.
The need for effective foam control in the paper industry generally, and in alkaline pulp-making processes in particular, has prompted the development of many different defoamer compositions. Considerable commercial success has been enjoyed in recent years by hydrophobic particle-containing defoamers, such as the hydrophobic silica-containing compositions described by Boylan in U.S. Pat. Nos. 3,076,768 and 3,408,306. Typically, hydrophobic particle defoamers are produced as mineral oil dispersions comprising upwards of 80% oil by weight. In common with other petroleum-based compositions, oil base defoamers have a number of drawbacks: flammability, relatively stringent labeling, shipping and storage requirements, and special, bothersome clean-up procedures for shipping containers, handling equipment and spills. In addition, carry-through of oil into process effluents poses potentially severe environmental problems, and increased petroleum costs resulting from the recent oil "crisis" makes oil-based products less attractive from a cost/performance standpoint.
Accordingly, one object of the present invention is to provide novel water-based defoamer compositions free from the drawbacks of prior art oil-based compositions.
In the soda and kraft pulping processes, commonly referred to as alkaline pulping processes, wood chips are cooked at elevated temperature and pressure in a solution composed of sodium hydroxide (soda process), or sodium hydroxide and sodium sulfate (kraft process). After draining off the spent cooking liquid, called black liquor because of its appearance, the resulting fiber suspension, or pulp, is washed substantially free of residual black liquor in multi-stage, countercurrent brown stock washers. The washed pulp is then screened to remove knots, incompletely cooked fiber clumps, and other foreign material.
Black liquor has a strong tendency to foam, even in dilute concentrations. Because of this, the control of foaming in black liquor-containing liquids is a common problem in alkaline pulp mills. Especially severe difficulties are often experienced in controlling foam in the initial or first stage brown stock washers. The black liquor in the first stage washers typically has a pH of about 12, a temperature of 165.degree.-185.degree. F., and a Baume' of about 10-14. Prior art defoamers have generally lacked the ability to control foaming in these washers except at undesireably high (and thus uneconomical) addition rates.
Accordingly, another object of the invention is to provide improved defoamer compositions which are especially adapted to control foaming of high temperature, high pH black liquor in soda and kraft brown stock washers.
Still another object of the invention is to provide improved defoamer compositions affording effective, economical foam control in these and other alkaline pulping process steps or operations.
A further object of the invention is to provide improved water-based defoamers in the form of pumpable liquids which can be readily mixed or dispersed in aqueous pulp and paper processing systems to control foam quickly and efficiently, and which improve liquid drainage and pitch dispersal in the pulp and paper stock.
Additional objects will become apparent from the detailed description set forth below. It will be understood, however, that the invention is not limited to the specific examples given to illustrate certain preferred embodiments.
In accordance with the present invention, improved water-based defoamer compositions are provided for controlling foaming in aqueous systems, and particularly in pulp and paper mill systems. Such compositions consist of an aqueous emulsion containing a moderate amount, i.e., about 20% to 30% by weight, of a composition comprised of about 25% to 55% of a water insoluble liquid hydrocarbon, about 25% to 55% of a normally solid fatty acid diamide, about 1.0% to 7.5% of hydrophobic silica particles, and about 8% to 16% of a non-ionic emulsifier having an HLB of about 8 to 12, with the percentages being based on the weight of the composition. In certain applications a portion of the fatty acid diamide may be replaced with a silicone oil to enhance "knock-down" of foam in the system. The novel water-based defoamer compositions of the invention are suitable for controlling foaming in a wide variety of aqueous systems, such as alkaline black liquor-containing pulp mill systems and acidic white water papermaking process streams.